Image scanning device and its control method

ABSTRACT

This invention provides a technique which allows more faithful color reproduction by a relative simple arrangement. To this end, according to this invention, by time-divisionally driving R, G, B, and E LEDs respectively having dominant emission wavelengths of 630 nm, 525 nm, 470 nm, and 500 nm, a common monochrome line image sensor ( 102 ) scans a document image. Scanned image data of respective color components undergo correction equivalent to that attained by shifting the barycentric positions of respective wavelength distributions so as to become closer to the CIE-RGB sensitivity distributions.

FIELD OF THE INVENTION

The present invention relates to a technique for scanning a documentimage, and outputting it as a digital image signal.

BACKGROUND OF THE INVENTION

Normally, an image scanning device represented by a color image scannerand the like has light sources (e.g., LEDs) with emission wavelengthcharacteristics of red (R), green (G), and blue (B), and scansinformation from a document using a common monochrome line image sensorwhile switching the ON/OFF states of them, and obtains two-dimensionalimage information while moving the monochrome line image sensor ordocument in a direction perpendicular to the arrangement direction ofdetection elements of the monochrome line image sensor (normally calleda sub-scan direction) (e.g., Japanese Patent Laid-Open No. 2003-315931).

The luminous spectrum characteristics of the LEDs of respective colorsas R, G, and B light sources used in the image scanning device areapproximately as shown in FIG. 3.

On the other hand, the luminousity characteristics of human eyes havespectral sensitivity characteristics different from the emissionwavelength characteristics of the LEDs, as shown in the CIE-RGBcalorimetric system color matching functions shown in FIG. 4.

In order to compensate for these differences, the scanned image dataundergoes color correction processes to improve color reproducibility ofthe scanned image. However, high color reproducibility has not beenobtained yet.

Especially, an image scanning device using only R, G, and Blight-emitting members cannot express a negative stimulus value of a redcomponent which appears near a wavelength of 500 nm in the CIE-RGBcolorimetric system color matching functions. Hence, the colorreproducibility of an emerald system is prone to be poor.

In order to express a color that cannot be expressed by the scanningmeans using only R, G, and B primary colors, a method of extracting acolor different from R, G, and B is known (Japanese Patent Laid-Open No.2003-284084). This method is applied to a two-dimensional image sensoradopted in a digital camera, and detects one pixel by a plurality oftypes of extraction units which are limited to the wavelength ranges ofR, G, and B and emerald color in place of switching light source colorsso as to obtain color information from an object.

However, according to the technique of this reference, since data forone pixel is extracted by extraction units of independent colors, thelight-receiving area of each extraction unit becomes too small to obtaina sufficient light-receiving amount. This imposes an influence on theS/N ratio. In addition, higher cost is required to manufacture suchimage sensing element, and it is difficult to apply this method to theimage scanning device.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the aboveproblems, and has as its object to provide a technique which can achievemore faithful color reproduction by a relative simple arrangement.

In order to solve the above problems, an image scanning device of thepresent invention comprises the following arrangement.

That is, there is provided an image scanning device comprising:

-   -   an illumination unit for illuminating a document while        selectively turning on visible light beams of at least four        colors in turn;    -   an image scanning unit for scanning the document image        illuminated by the illumination unit and outputting image data        of respective colors;    -   a moving unit for relatively moving the document image and the        image scanning unit; and    -   a control unit for, when the image scanning unit executes scan        processes of the document image for respective colors while        performing relative movement by the moving unit, controlling not        to successively execute the scan process of a first color having        highest spectral luminous efficacy among the visible light beams        of at least four colors and the scan process of a second color        having second highest spectral luminous efficacy.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a schematic sectional view of an image scanning deviceaccording to an embodiment of the present invention;

FIG. 2 is a flowchart showing the processing sequence of the imagescanning device according to the embodiment of the present invention;

FIG. 3 shows the luminous spectrum characteristics of R, G, and B LEDs;

FIG. 4 shows the CIE-RGB colorimetric system color matching functions;

FIG. 5 is a block diagram showing principal part of an image processingcircuit shown in FIG. 2;

FIG. 6 shows the luminous spectrum characteristics after correction ofthe first embodiment;

FIG. 7 is a block diagram of an image scanning device of the firstembodiment;

FIG. 8 is a timing chart upon scanning of the image scanning device ofthe first embodiment;

FIGS. 9A and 9B are flowcharts showing the setting processing sequenceof ON time data and shading correction data of the first embodiment;

FIG. 10 shows the luminous spectrum characteristics after correction ofthe second embodiment;

FIG. 11 is a schematic sectional view of a device which scans atransmitting document and is to be applied to the second embodiment;

FIG. 12 shows the luminous spectrum characteristics of R, G, B, and ELEDs in the second embodiment;

FIG. 13 is a functional block diagram of a scanner driver which runs ona host computer in a modification of the second embodiment;

FIG. 14 shows color difference characteristics of 3- and 4-color scanmodes;

FIG. 15 is a flowchart showing the processing contents of the scannerdriver in the modification of the second embodiment; and

FIGS. 16A and 16B respectively show a case wherein E and G componentsare successively scanned, and a case wherein E and G components arescanned every other colors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail hereinafter with reference to the accompanying drawings. Notethat LEDs as R, G, and B light sources in embodiments respectively havedominant emission wavelengths of 630 nm (R LED), 525 nm (G LED), and 470nm (B LED). These characteristics are not special but general LEDcharacteristics.

In the arrangement using such R, G, and B LEDs, some colors aredifficult to express. Especially, the CIE-RGB colorimetric system colormatching functions include a negative stimulus value of a red componentwhich appears near a wavelength of 500 nm, as shown in FIG. 4, and it isdifficult to express this color by three colors, i.e., R, G, and B.Hence, this embodiment will exemplify a case wherein an emerald LEDwhich has a dominant emission wavelength near 500 nm is arranged. Theluminous spectrum characteristics of the four-color LEDs (R, G, B, andE) in this embodiment are as shown in FIG. 12.

First Embodiment

FIG. 1 is a schematic sectional view of a document scanning device(image scanner) of this embodiment.

Referring to FIG. 1, reference numeral 101 denotes a contact imagesensor unit (to be abbreviated as CIS hereinafter). Reference numeral104 denotes an optical waveguide light source in which a red LED(R-LED), green LED (G-LED), blue LED (B-LED), and an emerald LED(emerald color will be referred to as E color hereinafter, and theemerald LED will be referred to as E-LED hereinafter) are arranged atthe end portion of the waveguide which is elongated in a directionperpendicular to the plane of page (main scan direction), and whichguides light emitted by each LED in the main scan direction by internalreflection to linearly irradiate a document 106 to be scanned on adocument table glass (platen glass) 105 with that light.

Light reflected by the document surface is received by a monochromeimage sensor 102 via a lens array 103. Light-receiving elements of themonochrome image sensor line up in the main scan direction. In theoptical waveguide light source 104, the R-LED is driven to emit light,and that light is received by the monochrome image sensor 102, thusscanning R component data for one line. Then, the G, B, and E LEDs aretime-divisionally driven to emit light, thus scanning G, B, and E datafor one line. The same process is repeated by moving the CIS 101 along aguide (not shown) in the sub-scan direction at a constant speed by thereciprocal number of the scan resolution in the sub-scan direction insynchronism with the time (line scan time) required to scan four colors,thereby obtaining two-dimensional image data.

Reference numeral 107 denotes an electronic circuit board which isarranged in the image scanning device, and mounts circuits to bedescribed later. The circuit board 107 is electrically connected to theCIS 101 via a flexible cable 108.

FIG. 7 is a block diagram when viewed from the electrical system of theimage scanning device of this embodiment. The same reference numerals inFIG. 7 denote the same parts as in FIG. 1.

Referring to FIG. 7, reference numeral 200 denotes a controller forcontrolling the overall device. The controller 200 also makes controlthat pertains to communications with an external host computer 300.

An analog electrical signal photoelectrically converted by the CIS 101is converted into a digital electrical signal by an AFE circuit 201including a sample/hold circuit such as CDS (correlative double samplingcircuit) and the like after it undergoes gain adjustment and DC offsetadjustment. A shading correction circuit 202 corrects the lightdistribution characteristics of an optical system. That is, the shadingcorrection circuit 202 stores, as shading correction data, referencelevel data which is generated by scanning light reflected by a whitereference plate (not shown) arranged outside the scan document range bythe CIS 101, and performs shading correction of image data generated byscanning the document to be scanned on the basis of this correctiondata. Note that the shading correction data may be output to and savedby the host computer 300 as an external apparatus, and data required forscan may be downloaded from the host computer 300 to the image scanningdevice upon executing processes.

An image processing circuit 203 performs predetermined processes ofimage data such as a gamma conversion process, a packing processaccording to an image scan mode (binary, 24-bit multi-valued, and thelike) which is set in advance by the host computer 300, and the like.When “binary” is set as the scan mode, a document image is scanned bydriving only the G-LED, and the image processing circuit 203 binarizesand outputs the scanned data. When “32-bit multi-valued” is designated,four R, G, B, and E LEDs are sequentially driven to perform imageprocesses (to be described later) for respective lines, i.e., in theorder of 1-line data of an R component, 1-line data of a G component,1-line data of a B component, and 1-line data of an E component to havea pixel of each of R, G, B, and E components as 8-bit data, and theprocessed data is output to the host computer 300.

An interface circuit 250 exchanges control signals and outputs an imagesignal with the host computer 300 such as a personal computer or thelike. In this embodiment, the interface circuit 250 comprises a USBinterface circuit. However, a SCSI interface circuit may be used. Thatis, the present invention is not limited in terms of the types ofinterfaces.

An LED driver 204 outputs drive signals of the four, i.e., R, G, B, andE LEDs included in the optical waveguide 104 in the CIS 101 under thecontrol of the controller 200. A motor driver 205 generates a drivesignal to a motor 206 which moves the CIS in the sub-scan direction.

Reference numeral 207 also denotes an LED driver which is used to turnon a transmitting document illumination unit 210 (including a lightsource) which is connected via an interface 208 to scan a transmittingdocument such as a positive/negative film or the like.

The process of the image scanning device of this embodiment will bedescribed below with reference to the flowchart of FIG. 2. Note that aprogram associated with FIG. 2 is stored in a ROM (not shown) in thecontroller 200.

Upon completion of initialization after power ON, the control waits forthe scan mode designated by the host computer 300 as an externalapparatus (strictly speaking, a scanner driver which is running on thehost computer 300). The scan mode includes a binary mode (scan mode byonly the G-LED), a 24-bit multi-valued mode (scan mode using three,i.e., R, G, and B LEDs), and a 32-bit multi-valued mode (scan mode usingfour, i.e., R, G, B, and E LEDs). Upon reception of a designationcommand of one of these modes, setups are made accordingly (step S801).

In step S802, the control waits for reception of a pre-scan startinstruction. Upon reception of a pre-scan start instruction request fromthe host computer 300, the control inquires the host computer 300 as towhether or not it holds LED ON time data and shading correction data,and checks based on its response if the host computer 300 stores thesepieces of information. As a result, if the host computer 300 stores theLED ON time data and shading correction data, the control requires thehost computer 300 of the LED ON time data and shading correction data,and downloads them to this image scanning device to make various setupsin step S804.

On the other hand, if it is determined in step S803 that the hostcomputer 300 does not store any LED ON time data and shading correctiondata, the flow advances to step S805 to generate LED ON time data andshading correction data. FIG. 8 is a timing chart of the generationprocess of the LED ON time data and shading correction data in stepS805, and FIGS. 9A and 9B shows the processing sequence of that process.The generation process will be described below with reference to thesefigures. Note that a case will be explained below wherein “32-bitmulti-valued” is designated as the scan mode.

In step S1001, the output signal from the monochrome image sensor 102 isread as black shading correction data while all the LEDs are OFF, and isset in the external apparatus (host computer) 300. With this setup,offsets, variations, and the like for respective pixels due to themonochrome image sensor 102 can be corrected.

Next, the LED ON times of respective colors are determined.

In step S1002, only the R-LED is turned on for predetermined ON time T0within which the scan signal level from the monochrome image sensor 102does not exceed a reference level set in the AFE circuit 201, and lightreflected by the white reference plate is scanned by the monochromeimage sensor 102.

It is checked in step S1003 if the scanned signal level has reached thereference level. As a result, the scanned signal level has not reachedthe reference level, the flow advances to step S1004 to increment anR-LED ON time by a predetermined value ΔT, and light reflected by thewhite reference plate is scanned again. In this way, the ON time isgradually increased, and if it is determined that the reference levelhas been reached, the LED ON time at that time is set as an ON time uponscanning an image for one line of the R-LED.

The ON times of the remaining G-, B-, and E-LEDs are determined bysubstantially the same processes. That is, steps S1006 to S1009 areprocesses for determining the ON time of the G-LED, steps S1010 to S1013are processes for determining the ON time of the B-LED, and steps S1014to S1017 are processes for determining the ON time of the E-LED.

After the ON times of the LEDs of all the color components aredetermined, the flow advances to step S1018 to scan light reflected bythe white reference plate for the LED ON times determined incorrespondence with R, G, B, and E, and white shading correction data isoutput to and is stored and held by the host computer 300.

The processes executed when the scan mode is the “32-bit multi-valued”mode have been explained. In the “24-bit multi-valued” mode, theprocesses in steps S1014 to S1017 are skipped since they are notrequired. In the “binary” mode, the processes in steps S1002 to S1005and S1010 to S1017 are skipped since only the G-LED is turned on andthese processes are not required.

Step S805 in FIG. 2 has been explained. Upon completion of the setups ofthe LED ON time data and shading correction data, the flow advances tostep S806.

In step S806, a pre-scan is executed. The pre-scan is a preliminary scanoperation, and scans a document image at a resolution lower than a finalscan (main scan) so as to inform the user of an overview of the scannedimage to some extent. Hence, the scan speed in the pre-scan (the movingdirection of the CIS 101 in the sub-scan direction) is higher than thatin the main scan.

This scan process will be explained below with reference to the timingchart in FIG. 8.

The R-LED is turned on while moving the CIS 101 in the sub-scandirection, and the monochrome image sensor 102 scans a document to bescanned only for one line. That is, red light reflected by the documentto be scanned is accumulated on the monochrome image sensor 102. Uponcompletion of the accumulation time for one line, the G-LED is turned onin turn. During this period, the scan signal for one line in the mainscan direction of the R component accumulated so far is output from themonochrome image sensor 102 as an output signal, which is output to thehost computer 300 via respective circuits. Likewise, the B-LED is turnedon, and G data is output during the B accumulation time. After that, theE-LED is turned on, and B data is output during the E accumulation time.Upon completion of the ON time of the E-LED, the CIS 101 has moved by awidth for one line in the sub-scan direction from the ON start positionof the R-LED. The R-LED is turned on to scan the next line. The Ecomponent data for the current line is output during the ON time(accumulation time) of the R-LED for the next line.

As a result, in the scan process in the scan mode (32-bit multi-valuedmode) using the four, i.e., R, G, B, and E LEDs, when the CIS 101 islocated at a given position, R, G, B, and E data are output to the hostcomputer 300 for one line. In the binary scan mode, every time a Gcomponent for one line is scanned, the CIS 101 is moved by a 1-linewidth in the sub-scan direction.

The aforementioned processes are executed until it is determined in stepS807 that scans for designated lines are complete. As a result, the usercan confirm an overview of a pre-scanned document image on the hostcomputer 300.

It is then checked in step S808 if a main scan request command isreceived. Upon reception of this request command, a scan process for oneline is executed in step S809, and this process is repeated until it isdetermined in step S810 that the scan processes for designated lines arecomplete. The differences between the main scan and pre-scan are asfollows. That is, the main scan scans according to the scan resolutionset by the user, while the pre-scan scans by decreasing the number ofdata per line compared to the main scan by decimating appropriate pixelsignals output from the monochrome image sensor 102. Also, the main scannarrows down the 1-line width of movement of the CIS 101 in the sub-scandirection than that in the pre-scan. In other words, the main scan scansat a higher resolution, while the pre-scan scans at a relatively lowerresolution since an overview of an image need only be recognized.

The image scanning device of this embodiment has been explained. Theprocesses in the image processing circuit 203 in this embodiment will beexplained below.

FIG. 5 is a block diagram showing principal part of the image processingcircuit 203 in this embodiment.

A color correction processor 801 multiplies raw image data scanned bythe image scanning device of this embodiment by color correctionprocessing coefficients according to the selected scan mode (to bedescribed in detail later). A tone adjustment processor 802 adjustslightness. An effect processor 803 applies effect processes forimproving image quality such as an edge emphasis process, noisereduction process, and the like, and outputs a final image.

The color correction processor 801 will be described in more detailbelow.

The pre-scan or main scan instruction request and the scan modedesignation are received from the host computer, as has been describedabove. This scan mode is also set in the color correction processor 801.This is to attain matching between the sender side (image scanningdevice) of image data and the receiver side (scanner driver).

If the scan mode is the binary mode, since one pixel is expressed by 1pixel, the tone adjustment processor 802 and effect processor 803 do notexecute any processes, and image data is directly output.

On the other hand, if the 24-bit multi-valued mode is set as the scanmode, the color correction processor 801 executes the followingprocesses. In the following description, Rc, Gc, and Bc indicatecorrected data, and data without any suffixes indicate data from theshading correction circuit 202.Rc=0.927×R+0.177×G−0.104×BGc=−0.013×R+1.204×G−0.191×BBc=−0.023×R−0.049×G+1.072×B  (1)

The above equations will be explained in more detail. As describedabove, the LEDs as the R, G, and B light sources in this embodimentrespectively have dominant emission wavelengths of 630 nm (R LED), 525nm (G LED), and 470 nm (B LED), as shown in FIG. 3. By contrast, in theluminousity characteristics of human eyes, the barycentric position of Rcomponent sensitivity is approximately 620 nm, that of G componentsensitivity is approximately 545 nm, and that of B component sensitivityis approximately 450 nm, resulting in differences between colorcomponents of the human eye and LEDs.

In other words, it is desired to shift the wavelength of an R componentobtained from the shading correction circuit 202 toward the shortwavelength side, that of a G component toward the long wavelength side,and that of a B component toward the short wavelength side.

However, R, G, and B data output from the shading correction data 202 donot include any wavelength components by now but include only theirlight-receiving intensities. Hence, data of the color components R, G,and B are considered as wavelength data since the magnitude relationshipof their wavelengths meet B<G<R, and correction substantially equivalentto movement of their barycentric positions is attained by multiplying R,G, and B by weighting coefficients and adding/subtracting them to/fromeach other, i.e., operating R, G, and B as composite wavelengthcomponents. That is, in order to shift an R component toward the shortwavelength side, the data value of an input R component is decreased,and values to be added to G and B components are increased. In order toshift a G component toward the long wavelength side, the ratio ofincreasing the G component is set to be large, and the ratio ofsubtracting the value of a B component is set to be large. Equations (1)above are derived as a result of examinations of various corrections andcolor reproducibilities on the basis of consideration of suchcorrelation among R, G, and B. According to equations (1) above, it wasdemonstrated that the LED luminous spectrum characteristics shown inFIG. 3 become nearly equivalent to those which have undergone correctionshown in FIG. 6.

As shown in FIG. 6, since the ratio of the red component that becomesinvolved with the green component increases, the same effect as thatobtained when the barycentric position of the luminous spectrumcharacteristics (luminous spectrum distribution) of the R componentshifts (moves) toward the short wavelength side is obtained. Also, thesame effect as that obtained when the G component shifts (moves) towardthe long wavelength side, and the same effect as that obtained when theB component shifts (moves) toward the short wavelength side areobtained. That is, after the arithmetic operations of equations (1), thebarycentric positions of the R, G, and B components have moved to thevicinities of 620 nm, 530 nm, and 470 nm, and the characteristicsapproximate to CIE-RGB shown in FIG. 4 can be obtained. As describedabove, by making the arithmetic operations given by equations (1), uponscanning in the 24-bit multi-valued mode, color reproducibility higherthan that obtained without any correction can be obtained.

On the other hand, if the 32-bit multi-valued mode is set, the colorcorrection processor 801 converts data of color components R, G, B, andE into R, G, and B component data that can be used by the personalcomputer via equations (2) below. In equations (2), data with suffixes“c” indicate converted data, and data without any suffixes indicateinput color component data.Rc=0.947×R+0.192×G−0.119×B−0.018×EGc=−0.020×R+1.972×G+0.031×B−0.983×EBc=−0.023×R+0.127×G+1.080×B−0.184×E  (2)

FIG. 10 shows the luminous spectrum characteristics equivalent to theseconversion results. As shown in FIG. 10, since the E-LED is used, andthe correction based on equations (2) is applied, the barycentricposition of the red luminous spectrum characteristics shifts toward theshort wavelength side, and can become closer to that of the luminousspectrum characteristics of a red component of CIE-RGB compared to thecorrection of equations (1). As for a green component, an emeraldwavelength component of the green component is largely subtracted, ascan be seen from FIG. 10. Furthermore, the half wavelength of the greencomponent on the short wavelength side shifts from the vicinity of 500nm to that of 510 nm, and the barycentric position of the luminousspectrum characteristics shifts toward the long wavelength side andtends to be closer to that of the luminous spectrum characteristics ofthe green component of CIE-RGB.

As described above, in the 32-bit multi-valued image scan mode using thefour, i.e., R, G, B, and E LEDs, the LED luminous spectrumcharacteristics can be precisely approximate to those of CIE-RGB, thusfurther improving the color reproducibility.

In this embodiment, the four-color scan mode is made in the order of R,G, B, and E as shown in FIG. 8 upon focusing attention on one line to bescanned for the following reason.

E component data described in this embodiment has a large overlapwavelength range with the G component of the R, G, and B components, ascan be seen from FIG. 12. That is, the E component data has a highestcorrelation coefficient with the G component. When conversion from fourcolors into three colors based on equations (2) is made, G componentdata after three-color conversion is mainly generated from G and Ecomponents before conversion. Also, the human eye have a highestspectral luminous efficacy with respect to the G component whichincludes a wavelength of 555 nm as nearly the center of the visiblelight range.

FIG. 16A shows a case wherein E and G components are scannedsuccessively, and FIG. 16B shows a case wherein E and G components arescanned every other colors. As shown in FIG. 16A, when E and Gcomponents are successively scanned, the sampling period in the sub-scandirection with respect to colors in the overlap wavelength range of theE and G components becomes equal to those of R and B components.However, when the E and G components are scanned every other colors, thesampling period in the sub-scan direction is raised with respect tocolors in the overlap wavelength range of the E and G components.

In this way, since the control is made not to successively scan a Gcomponent to which the human eye has a highest spectral luminousefficacy and an E component having high correlation with the G componentand having a second highest spectral luminous efficacy, i.e., to scan Eand G components every other color components, the resolution in thesub-scan direction can be improved with respect to colors in the overlapwavelength range of the E and G components. Therefore, as the scan orderof respective color components, an R or B component is preferablyscanned between G and E components. More specifically, the control ispreferably made to scan by turning on the color LEDs in the order of R,G, B, and E described in this embodiment or in the order of R, E, B, andB.

Second Embodiment

In the first embodiment, the color correction processes in thethree-color scan mode and four-color scan mode are executed on the imagescanning device side. Alternatively, the scanned R, G, and B or R, G, B,and E component data may be output to the host computer, which mayexecute the correction processes. When the correction processes are doneon the host computer side, that correction function can be added to animage scanner driver which runs on the host computer. As a result, theedit processes that can obtain the effects of the above embodiment canbe made without modifying a normal image processing application.

An implementation example of the color correction processes by a scannerdriver on the PC 300 side will be explained hereinafter as the secondembodiment.

The structure of the image scanning device is the same as that shown inFIG. 7. However, when the 32-bit multi-valued mode is set, the imagescanning device directly outputs 8-bit data of R, G, B, and E componentsto the PC 300.

FIG. 13 is a functional block diagram of a part that pertains to imagereception of a scanner driver which runs on the host computer 300 inthis modification (a GUI part used to issue commands to the imagescanning device, and a processing part that pertains to transmission ofLED ON time data and shading correction data are not shown).

A color correction processor 1101 multiplies raw image data scanned bythe image scanning device of this embodiment by color correctionprocessing coefficients according to the selected scan mode (to bedescribed in detail later). A tone adjustment processor 1102 adjustslightness. An effect processor 1103 applies effect processes forimproving image quality such as an edge emphasis process, noisereduction process, and the like, and outputs a final image to anapplication as a read source (in general, an image edit application orthe like).

The color correction processor 1101 will be described in more detailbelow.

Upon transmitting the pre-scan or main scan instruction to the imagescanning device, the scan mode is set in the image scanning device, ashas been described above. This scan mode is also set in the colorcorrection processor 1101. This is to attain matching between the senderside (image scanning device) of image data and the receiver side(scanner driver).

If the scan mode is the binary mode, since one pixel is expressed by 1pixel, the tone adjustment processor 1102 and effect processor 1103 donot execute any processes, and image data is directly output to anapplication.

On the other hand, if the 24-bit multi-valued mode (three-color LED scanmode) or 32-bit multi-valued mode (four-color LED scan mode) is set asthe scan mode, the color correction processor 1101 executes thefollowing processes. In the following description, Rc, Gc, and Bcindicate corrected data, and data without any suffixes indicate raw datafrom the image scanning device.

-   -   In case of 24-bit multi-valued mode:        Rc=0.927×R+0.177×G−0.104×B        Gc=−0.013×R+1.204×G−0.191×B        Bc=−0.023×R−0.049×G+1.072×B  (3)    -   In case of 32-bit multi-valued mode:        Rc=0.947×R+0.192×G−0.119×B−0.018×E        Gc=−0.020×R+1.972×G+0.031×B−0.983×E        Bc=−0.023×R+0.127×G+1.080×B−0.184×E  (4)

As a result of the above processes, in either of the 24- or 32-bitmulti-valued mode, conversion to three primary colors, i.e., R, G, and Bdata expressed by a personal computer or the like is made.

FIG. 15 is a flowchart showing an example of the reception process ofimage data in the scanner driver program of this embodiment.

It is checked in step S1 if the scan process has been made in the binaryscan mode. If it is determined that the scan process has been made inthe binary scan mode, the flow advances to step S2 to receive binarydata for one line. In step S3, the binary data is output to anapplication which has launched this scanner driver.

On the other hand, if it is determined that the scan process has beenmade in the three- or four-color LED scan mode, R, G, and B data for oneline are received and are stored in an appropriate area of a RAM of thehost computer in steps S4 to S6. If the three-color LED scan mode isdetermined in step S7, the flow advances to step S8 to apply thecorrection processes based on equations (3) above. On the other hand, ifthe four-color LED scan mode is determined, the remaining E data isreceived in step S9, and the correction processes based on equations (4)above are applied in step S10.

After that, tone adjustment is applied in step S11, and the effectprocess is applied in step S12. In step S13, the R, G, and B data areoutput to the application which has launched this scanner driver.

In this manner, image data for one line is output to the application. Itis checked in step S14 if data for the number of lines designated by thescan instruction have been received. If NO in step S14, the processes instep S1 and subsequent steps are repeated.

The present inventors confirmed the presence of the followingdifferences in association with the color reproducibility of R, G, andB, three-primary-color scanned image data and that of four-color scannedimage data.

Image data, which are obtained by scanning “IT8 chart” normally used forcolor calibration of input and output devices in the 24- and 32-bitmulti-valued modes using the image scanning device of this embodiment,are corrected by the aforementioned processes to generate R, G, and Bimage data of three, R, G, and B components, and the R, G, and B imagedata are converted into image data on the Lab color space via the XYZcolor space. Color conversion colors used in this case are as follows(note that the light source is of D65 type):X=0.4124×Rc+0.3576×Gc+0.1805×BcY=0.2126×Rc+0.7152×Gc+0.0722×BcZ=0.0193×Rc+0.1192×Gc+0.9505×BcL=116×(Y/Y0)^(0.333)−16a=500×[(X/X0)^(0.333)−(Y/Y0)^(0.333)]b=200×[(Y/Y0)^(0.333)−(Z/Z0)^(0.333)]  (5)

-   -   for X0=0.95045, Y0=1.0, and Z0=1.08906.

A color difference ΔE is calculated from the L, a, and B image datacalculated using equations (5) and the colorimetric values of the IT8chart. The color difference ΔE is given by:ΔE=(ΔL ² +Δa ² +Δb ²)^(1/2)where ΔL, Δa, and Δb are the differences between the image data obtainedby the image scanning device of this embodiment, and calorimetric dataof a document.

FIG. 14 shows the comparison results of representative colors (red,green, blue, emerald, magenta, yellow) of the color differences ΔE ofthe three- and four-color scan modes, which are calculated by the aboveformula. As shown in FIG. 14, red, green, and blue have substantially nodifferences or small differences between the three- and four-color scanmodes. However, emerald, magenta, and yellow have smaller colordifferences in the four-color scan mode than the three-color scan mode.Especially, as seen easily, “emerald (E component)” as the fourthlight-emitting member has a large difference, and the four-color scanmode has higher color reproducibility.

In the above example, in the three- and four-color scan modes, the hostcomputer performs conversion and correction to R, G, and B data.Alternatively, the image scanning device may perform such conversion andcorrection. In this case, the load on the image scanning device becomesheavier and line buffers for four colors (required to calculate R. G,and B data) must be added. However, the host computer can exploit anexisting three-color scanner driver. Note that since the existingscanner driver cannot designate the four-color scan mode, a controlpanel or the like equipped on the image scanning device must be used todesignate that mode.

As described above, according to this modification, the image scanningdevice shown in FIG. 11 and the host scanner driver program on the hostcomputer 300 can obtain an image with high color reproducibility. Hence,since the scanner driver program on the host computer implements theaforementioned processes, the scope of the present invention includessuch computer program. Normally, since the computer program is stored ina computer-readable storage medium such as a CD-ROM or the like, whichis set in a reader of the computer, and is ready to run when the programis copied or installed in the system, the scope of the present inventionalso includes such computer-readable storage medium.

Third Embodiment

A case will be explained below wherein the transmitting documentillumination unit 210 (see FIG. 7) is used. The transmitting documentillumination unit 210 includes four LEDs, i.e., R, G, B, and E LEDs ifit is applied to the first embodiment.

Nowadays, a four-layered silver halide film to which a color sensitivelayer sensitive to emerald is added in addition to red, green, and bluecolor sensitive layers is commercially available, as disclosed inJapanese Patent Laid-Open No. 2003-84402. Since the transmittingdocument illumination unit 210 of this embodiment includes four, R, G,B, and E light sources (LEDs) as in the above description, it scans atransmitting document of such four-layered silver halide film, thusobtaining a scanned image with higher color reproducibility.

FIG. 11 is a sectional view when the transmitting document illuminationunit 210 is connected to the interface 208 of this device via a cable230. In FIG. 11, reference numeral 220 denotes a film holder which holdsa film to be scanned. The film holder has an opening (not shown) for oneframe of the film, and the transmitting document illumination unit 210is set above the holder. The transmitting document illumination unit 210includes an R light-emitting LED 210R, G light-emitting LED 210G, Blight-emitting LED 210B, and E light-emitting LED 210E, one of which isturned on as in the optical waveguide 104. Reference numeral 211 denotesa panel which two-dimensionally, uniformly emits light upon emission oflight by each LED, and has a size at least larger than that of one frameof the film. Since details of alignment and the like between the filmholder and transmitting document illumination unit are explained inJapanese Patent Laid-Open No. 2004-7547 that has already proposed by thepresent applicant, a description thereof will be omitted.

Upon detection of connection of the transmitting document illuminationunit 210 to this device (an appropriate switch is provided to theinterface 208, and detection is made based on the state of that switch),the controller 200 disables the optical waveguide 104, and determinesthe transmitting document illumination unit 210 as an object to bedriven.

Since the actual scan process is substantially the same as that in theabove embodiment except that the LEDs in the optical waveguide lightsource 104 are switched to those of the transmitting documentillumination unit 210, and movement in the sub-scan direction is made incorrespondence with the film size, a description thereof will beomitted.

As described above, upon scanning a four-layered silver halide film orthe like to which a color sensitive layer sensitive to emerald is addedin addition to normal R, G, and B color sensitive layer, the scanprocess of this embodiment can be performed by sufficiently utilizingthe film characteristics, thus obtaining a scanned image with highercolor reproducibility.

Note that the image scanning device of this embodiment has exemplifiedan image scanner as a peripheral device of the host computer, but may beapplied to a document scanner of a copying machine. When the imagescanning device of this embodiment is applied to the copying machine, aprint process is made after conversion RGBE→RGB→YMCK.

In this embodiment, the contact image sensor (CIS) has been exemplified.However, since the present invention can be applied to a device using aCCD, the present invention is not limited to the aforementioned specificembodiments. Furthermore, the present invention can be applied to notonly a device that scans a document image using four colors, but also adevice that scans a document image using five or more colors. Asdescribed above, according to the present invention, the colorreproducibility of a scanned image can be improved compared to theconventional document scan process using R, G, and B light-emittingmembers.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the claims.

CLAIM OF PRIORITY

This application claims priority from Japanese Patent Application Nos.2004-031404 and 2004-031405, both filed on Feb. 6, 2004, which is herebyincorporated by reference herein.

1. An image scanning device comprising: an illumination unit forilluminating a document while selectively turning on visible light beamsof at least four colors in turn; an image scanning unit for scanning thedocument image illuminated by said illumination unit and outputtingimage data of respective colors; a moving unit for relatively moving thedocument image and said image scanning unit; and a control unit for,when said image scanning unit executes scan processes of the documentimage for respective colors while performing relative movement by saidmoving unit, controlling not to successively execute the scan process ofa first color having highest spectral luminous efficacy among thevisible light beams of at least four colors and the scan process of asecond color having second highest spectral luminous efficacy.
 2. Thedevice according to claim 1, wherein said illumination unit turns on atleast red, green, blue, and emerald light beams, and said control unitcontrols said illumination unit to selectively turn on the light beamsof respective colors in an order of red, green, blue, and emerald orred, emerald, blue, and green.
 3. The device according to claim 1,wherein said illumination unit is integrated with said image scanningunit.
 4. The device according to claim 1, wherein said illumination unitincludes a unit which illuminates light from a back surface of adocument.
 5. The device according to claim 1, further comprising asetting unit for setting one of a first document scan mode forilluminating the document using said illumination unit while selectivelyturning on visible light beams of less than four colors, and scanningthe document image using said image scanning unit, and a second documentscan mode for illuminating the document using said illumination unitwhile selectively turning on visible light beams of at least fourcolors, and scanning the document image using said image scanning unit.6. The device according to claim 5, wherein said unit sets one of thefirst and second document scan modes in accordance with instructioninformation from an apparatus to which a scanned image is to be output.7. The device according to claim 1, further comprising an arithmeticunit for calculating composite wavelength component data by makingpredetermined arithmetic operations using as wavelength component dataimage data of respective colors obtained by scanning the document imageby said image scanning unit.
 8. A method of controlling an imagescanning method, which has an illumination unit for illuminating adocument while selectively turning on visible light beams of at leastfour colors in turn, an image scanning unit for scanning the documentimage illuminated by said illumination unit and outputting image data ofrespective colors, and a moving unit for relatively moving the documentimage and said image scanning unit, comprising a step of: controlling,when said image scanning unit executes scan processes of the documentimage for respective colors while performing relative movement by saidmoving unit, not to successively execute the scan process of a firstcolor having highest spectral luminous efficacy among the visible lightbeams of at least four colors and the scan process of a second colorhaving second highest spectral luminous efficacy.
 9. The methodaccording to claim 8, wherein said illumination unit turns on at leastred, green, blue, and emerald light beams, and said control unitcontrols said illumination unit to selectively turn on the light beamsof respective colors in an order of red, green, blue, and emerald orred, emerald, blue, and green.
 10. The method according to claim 8,further comprising a setting step of setting one of a first documentscan mode for illuminating the document using said illumination unitwhile selectively turning on visible light beams of less than fourcolors, and scanning the document image using said image scanning unit,and a second document scan mode for illuminating the document using saidillumination unit while selectively turning on visible light beams of atleast four colors, and scanning the document image using said imagescanning unit.
 11. The method according to claim 8, further comprisingan arithmetic step of calculating composite wavelength component data bymaking predetermined arithmetic operations using as wavelength componentdata image data of respective colors obtained by scanning the documentimage by said image scanning unit.
 12. A program for making a computerexecute a control method of an image scanning device of claim
 8. 13. Acomputer-readable storage medium storing a program of claim 12.